Use of modifiers systems in combination with anionic initiators in the polymerization of styrene/butadiene copolymers is well known. Such modifiers, however, both increase the 1,2-microstructure of the diene monomer contributed units of the copolymer finally produced and decrease the block styrene content.
Chelating modifiers including OOPS or TMEDA increase the 1,2-microstructure of the diene units of the copolymer finally produced. Non-chelating tertiary amine modifiers which remain with the polymers cause yellowing of the polymers during post polymerization processing such as extrusion and injection molding processes. Tetrahydrofuran (THF), a well-known non-chelating modifier, is known to react with C--Li bonds producing Li alkoxide. THF is difficult to remove from hydrocarbon polymerization media due to its low boiling point.
It is desirable to provide an anionic initiator/modifier system for preparing polystyrene having a narrow molecular weight distribution and for preparing block copolymers of styrene-butadiene having improved initiation rates without having their 1,2-microstructure affected by the presence of a modifier. It is also desirable to discover modifiers that are easily recoverable from solvent process streams.